This invention relates to synthesis of novel crystalline aluminosilicate zeolites. More particularly, this invention relates to a method of synthesizing a crystalline aluminosilicate zeolite from a reaction mixture containing an alkali metal compound, an amide compound, a silicon compound, an aluminum compound and water.
It may be generally said that zeolites are crystals of hydrated aluminosilicates of alkali metals and alkaline earth metals and structurally comprise a three-dimensional network of Si--O.sub.4 and Al--O.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms. Such crystalline zeolites have a crystalline structure within which there are channels, cations, molecules of water and mutually interconnected cavities. The molecules of water are normally dehydrated continuously or reversibly and the crystalline structure is not destroyed by said dehydration. Therefore, these crystalline zeolites are formed into porous adsorbents. As the pores of the crystalline zeolites have a uniform diameter of several .ANG., these crystalline zeolites act as molecular sieves to accept for adsorption only molecules whose molecular diameter is smaller than this pore diameter. Such crystalline zeolites are well known as molecular sieves, and various processes are industrialized taking advantage of these characteristics.
Crystalline aluminosilicate zeolites are basically synthesized by depositing crystals from a four-component system consisting of base, silica, alumina and water. Crystalline aluminosilicate zeolites have hitherto been synthesized in various methods, but recently a method has been developed wherein the base, one member of reactant materials, has been replaced partially with an organic base. This method is described on pages 304-312 of "Zeolite Molecular Sieves" by D. W. Breck (Wiley Inter Science published 1974). As the representative synthetic example thereof is well known a method wherein the reactant material, namely, the base, is exchanged partially by a primary amine or quaternary ammonium salt.
When synthesis is carried out according to the above mentioned method, there can be obtained crystalline aluminosilicate zeolites having a high SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio. Such crystalline aluminosilicate zeolites are known to exhibit enhanced thermal stability and acid resistance and to function as high active catalysts in catalytic cracking of hydrocarbons, alkylation isomerization and the like.
The inventors of this invention has carried out a series of studies to find that crystalline aluminosilicate zeolites having a high SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio can be synthesized by utilizing an alkali metal and an amide compound as the base constituting the reactant material.